Could you please assist me in determining what I should do if a company refuses to refund my money?

I purchased a wig for 300 pounds from a company called allove hair through Instagram. Since I was not satisfied with the item when it arrived, I requested a return. At first, they were hesitant to provide me with their address and offered me discounts, but I declined. I sent the wig back about 2 months ago and received a notification that it had been delivered to the address, however, the receivers claim that they hadn't received it. After contacting the delivery company, they conducted their own investigation and provided a slip of signature indicating that it had been received. After forwarding this evidence to the company, they have agreed to refund my money, however, they have not taken any action. My belief is that they are not going to refund me because they are aware that I live in the UK and will not be able to take action against them. 

I would appreciate it if you could advise me